17th ISHW Oct. 12, 2009, Princeton, NJ, USA

Effect of Nonaxisymmetric Perturbation on Profile Formation

I-08

T. Morisaki, Y. Suzuki, J. Miyazawa, M. Kobayashi, S. Masuzaki, M. Goto, R. Sakamoto, H. Funaba, N. Ohyabu, H. Yamada, A. Komori and LHD Experiment Group

National Institute for Fusion Science

Contents intrinsic edge stochasticity - introduction - enhanced stochasticity by plasma itself and external perturbation field - particle transport (density pump out) -

Introduction - edge stochastic region in LHD -

Heliotron configuration intrinsically has stochastic region

LK < Lc

sufficiently stochastic

Motivation - what about transport in stochastic region ? -

e rapidly increases where LK < ~ 50m - independent of magnetic configuration -

Energy flow seems to reflect the magnetic field topology

On the other hand….. No clear gradient change is seen Relatively high ne region spreads

across LCFS

Particles feel magnetic structure ?To see this in detail, experiments in various edge topology are necessary

Edge magnetic topology can be varied

Rax=3.6m

Rax=3.9m

outward shift

Stochastic region spreads over in outward shifted configuration

(1) by changing magnetic axis (2) by external magnetic perturbation

10 pairs of normal conducting coils can apply m/n=1/1 and 2/1 perturbations

Stochastization is enhanced in SDC plasma

* ne(0) ~ 1x1021 m-3

* Te(0) ~ 0.4 keV* P(0) ~ 140kPa* Wdia ~ 1MJ* (0) ~ 4.7%

SuperDense Core plasma with Internal Diffusion Barrier (IDB-SDC plasma)

strong edge pumping + central fuelling

high pressure core region ==> - large Shafranov shift steep gradient at IDB ==> - spontaneous current , e.g. bootstrap - destabilization of MHD activities

Edge stochasticity is enhanced(Furthermore, what if perturbation is applied to SDC plasma ?)

0=0%

1.86%

4.09%

As 0 increases .... HINT2 code predictions

b/BT=0%

Flux surfaces are sensitive to external perturbation, especially in high beta regime

b/BT=0.02% (m/n = 1/1)

(HINT2 can calculate 3D equilibrium even in the stochastic region)

Effect of external perturbation on ne, Te profiles

Applying m/n=1/1 perturbation, - ne in stochastic region is pumped out - Te at core region increases - enhanced stochasticity (HINT2)

gas puffw/o b

~

pellet

w/o b~

pump + pellet, - IDB-SDC plasma - ne at edge decreases - edge stochasticitization

w/ b~

b/BT=0.12% ~pellet

Temporal behavior of IDB-SDC plasma with strong perturbation

With perturbation, - higher P0 is obtained - smaller Wdia due to reduction of edge ne

pellet

Sudden decrease of P0 ~ 0.2 s after its peak - Core Density Collapse (CDC) -

w/b ne in mantle rapidly decreases soon after the final pellet (convex downward) ne in core stays for a while ==> suggesting different transport between core and mantle w/o b ne in whole region gradually decreases

w/o

w/ b~

mantle

core

pelletw/ b

~

w/o

w/o b~

Effect of perturbation on particle transport

Strong perturbation enhances edge particle transport ( not so in core) which is due to enhanced stochasticity in mantle with external perturbation (consistent with HINT2 prediction)

1D particle transport analyses

e

e e

1 nD v

n n r

e

0

1d

r nr S r

r t

w/ b~

Effect of perturbation on particle transport

Applying perturbation, grad ne becomes steep with b foot point is at r/a ~ 0.55 - 0.60 pump out effect is strong with strong b (detailed analysis is on going)

From LK calculation with HINT2 equilibria, stochasticity increases with b even a small b results in strong stochastization

ne pump out dependence on perturbation field strength

Even a small perturbation can pump out particles in mantle

Accordingly central pressure increase

suggesting that magnetic field in mantle is sensitive to external perturbation in SDC plasma(consistent with HINT2 calculation)

ne_mantle

ne_mantle

Recovery of D in mantle

At highest P0, D in mantle is high

After P0 drop, - D in mantle improves, suggesting the restoration of ergodized region - D in core still keeps low

Recovery of D in mantle

Drop of P0 returns the plasma back to the low regime with relatively “peaceful” magnetic flux surfaces

Recovery of D in mantle

Summary

Effect of externally applied low m/n magnetic perturbation on high density plasma

with peaked pressure profile is numerically and experimentally investigated.

Even with a small perturbation, magnetic surfaces are strongly deformed,

- which enlarges magnetic islands.

- which enhances the edge stochastization.

With strong perturbation, density pump out is observed in the mantle (edge) region, together with the increase of core Te (or P),

- degradation of particle transport (D) in the mantle, but not in the core.

Even a small perturbation can affect the profile formation

After the P0 drop, stochastized mantle is restored and D recoves

Power deposition profiles with and without perturbation

low edge ne (w/ perturbation)

Effect of external perturbation on ne, Te profiles

- edge stochasticity increases (HINT2 )

According to HINT2 calculation,edge region is ergodized in SDC

w/o b~

Applying m/n=1/1 perturbation, - ne in stochastic region is pumped out - Te at core region increases

w/ b~

b/BT=0.12% (m/n = 1/1)

~

Temporal behavior of IDB-SDC plasma with strong perturbation

With perturbation, - higher P0 is obtained - smaller Wdia due to reduction of edge ne

pellet

mantle

core

pellet

Sudden decrease of P0 ~ 0.2 s after its peak - Core Density Collapse (CDC) -

ne in mantle rapidly decreases soon after the final pellet (convex downward) ne in core stays for a while suggesting different transport between core and mantle

w/o

w/ b~